This invention generally relates to swash plate type axial piston machines and in particular to any machine with a rotating cylinder block comprising pistons, axial forces of which are transmitted on a swash plate by piston rods connected to a common sliding plate by spherical joints.
DE 40 24 319 discloses a hydraulic machine having a cylinder block with axial pistons and a swash plate supporting a sliding plate. The pistons are connected to piston rods by means of first spherical joints, the piston rods being connected to the sliding plate by means of second spherical joints. The angular position of the cylinder block with respect to the sliding plate is synchronized by a couple of bevel gears, respectively fixedly connected with the cylinder block and with the sliding plate. This bevel gearing can also transmit a portion of the torque developed by this piston machine. The disadvantage of this solution is that it is only usable for axial piston machines with a constant displacement volume because the bevels gears engage for a given inclination of the swash plate. Therefore, the inclination of the swash plate cannot be changed and this solution is not applicable for axial piston machines with a variable displacement volume (cylinder capacity).
Another solution for swash plate type axial piston machines is known by GB1,140,167 and is supposed to be usable with a variable displacement. With this solution, a synchronizing mechanism keeps the piston rods during their activity in a position, which is substantially perpendicular to a bearing surface of the sliding plate that is supported by the swash plate. This synchronization is obtained by slots made in a timing member fixed on the sliding plate and receiving the cylindrical piston rods. For each piston rod, the slot allows an unrestricted radial pivoting of the piston rod. During rotation of the cylinder block, a piston rod periodically abuts against one of the two parallel flat faces of the corresponding slot, so that this rod is maintained substantially perpendicular to the bearing surface of the sliding plate due to this contact between the cylindrical surface of the piston rod and the flat face of the slot. The contacting surfaces (that is the cylindrical surface of the piston rod and the flat face of the slot) have different profiles, so that the synchronization between the cylinder block and the sliding plate is significantly delayed. Furthermore, the manufacturing of the involved parts generates significant clearance increasing again the delay in synchronization. Therefore such a design delays the synchronization, generates higher loads in the piston rod and very high Hertzian contact pressures that may bring rapid pitting of the contacting surfaces.